For years, I’ve been telling travelers to pay with plastic and so have my buddies in the vacation punditry business.

Credit cards protect you from unscrupulous travel agents and tour operators. They hold companies accountable for substandard cruises, flights and hotel rooms. Plus, you can rack up more frequent-flier miles than you’ll ever be able to spend.

But what if the very payment system everyone swears by was quietly helping itself to your money, a few bucks at a time, when you travel? What if companies were quietly tacking new fees onto your bill when you were away?

No need to imagine. Let me introduce you to two fast-growing credit card surcharges: the foreign transaction fee and the airline ticket convenience fee.